Plastic bags of the type described here are typically comprised of a bag body folded to form top and bottom layers which are typically cut and sealed at the side edges. The front edges of the top and bottom layers, located opposite the fold, define the mouth of the bag. A near margin at the bag mouth is typically folded inside the bag to form a hem which is ordinarily sealed to the bag body to form a channel holding draw tapes. Pulling on accessible portions of the draw tapes causes the bag mouth to constrict thus closing the bag at its top.
Draw "string" bags have long been utilized, and have taken many forms. While drawstring bags made of plastic have been utilized to some extent, such bags have been used mostly in the lower volume boutique bag market because bags using draw "strings" tend to be more expensive. Much of the reason for this limitation in the market area is the cost of producing a draw "string" bag.
Manufacturing a plastic draw "string" bag typically requires special processing steps related to joining ends of the string being used. The string must be knotted, provided with a metal fastener, or otherwise fixed together at two ends in each such bag. Such processes cannot be carried out by the equipment usually associated with fabrication steps used to form seals and cuts in the plastic webbing from which the bag is derived. Accordingly, additional equipment must be used to so manipulate the draw "string," at related additional costs.
Subsequently, draw "tape" bags have been developed, first mostly in the boutique bag area, but now more generally for the higher volume markets. Draw tape bags represent a major advance in that a thermoplastic bag (e.g. low density polyethylene or linear low density polyethylene copolymer or the like) is provided with a thermoplastic tape (e.g. high density polyethylene), the tape being heat sealed into the bag during the process of manufacturing the bag. While draw "tape" bags in general represent a substantial improvement over draw "string" bags, there are still numerous difficulties in the production of the draw tape bags.
In making a draw tape bag in the conventional art, plastic film material is generally obtained in parent rolls. The roll is unwound and fed to a draw tape machine. The draw tape machine forms hems at edges of the web which ultimately form the top edges of the finished bag, and incorporates draw tape material into the hems, in addition to cutting holes at the edges which form the top edges of the finished bag. The hem is sealed, securing the tapes in the formed hems.
In the alternative, the plastic film material may be received in-line, from an ongoing film extrusion process.
In effecting the tape insertion, one or two strips of tape material are unwound from respective parent rolls and fed to the formed hems of the respective top and bottom layers. Accordingly, a draw tape machine must handle at least the main web which is used to form the plastic bag, as well as the one or two tape webs being inserted into the hems. Normally two sets of sealing bars or the like are required for forming the heat seals at the respective two hems after the tapes are inserted.
Finally, after the draw tape insertion process is completed, the web is transferred from the draw tape machine to a bag-forming machine where transverse side seals, and corresponding cuts, are made across the width of the plastic web, forming side seals and cutting the continuous web into individual bags, using conventional heat sealing and cutting equipment and methods. The steps that form the side seals and cut the sides of succeeding bags from each other also seal the draw tapes, in the hems, to the bag material, itself, along the side edges of the bags, as well as cutting the tapes to a length corresponding to the full widths of the bags being fabricated.
This invention focuses on the draw tape equipment. Web material processed in this invention is subsequently transferred to bag making equipment for further processing as into the finished individual bags. The equipment of the invention could readily be incorporated into the bag making machine such that the draw tape apparatus and bag making apparatus might be incorporated into one common frame and driven by a single common controller, integrating the several steps of the overall process of both the draw tape operation and the bag making and cutting operation. While such is certainly feasible with the invention as disclosed herein, the description herein focuses on the novel aspects of such apparatus which is in general defined in the draw tape equipment.
Early bag-making equipment was designed on the basis of intermittent motion. Namely the bag-making equipment would stop the plastic web for performing bag-making steps, whether for making side seals in the bags, cutting the bags apart from the web, or for performing one or more of the earlier steps such as those associated with forming hems at the top edge of the bags, or inserting tapes into such hems. After the desired step(s) were performed, transport of the bag was again started and the bag advanced to subsequent steps. More recently, continuous motion processing equipment has been developed wherein bag-making steps are performed while the bag advances continuously along a processing line.
However, even the most modern bag-making equipment still includes a variety of problems. Of particular concern in this invention is the apparatus used to form hems and incorporate draw tapes into the hems. There is also the issue of controlling the temperature of the parent web both before and after the hem sealing step. There is also the issue of minimizing the amount of floor space occupied by the bag forming machinery while retaining the web being processed where workers can reach it from floor level. Finally, there is the issue of improving handling of the parent web during its traverse through the bag forming operation.
It is an object of the invention to provide draw tape equipment and methods for forming hems around the draw tapes, rather than inserting the draw tapes into already-formed hems.
It is another object to provide draw tape draw tape equipment and methods wherein holes are formed adjacent the free edges of the plastic web before the free edges are folded for incorporation of draw tapes therein.
It is still another object to provide draw tape equipment and methods controlling the temperature of the parent web material both before and after applying sealing heat to formed hems.
It is yet another object to provide draw tape equipment and methods, separating edge regions of the top and bottom layers of the plastic and forming hem seals on both the top and bottom layers along parallel paths.
It is a further object of the invention to minimize the floor space occupied by the draw tape equipment while maintaining the web being processed at a level which can be reached by workmen standing on the floor of the work place.
Another object is to stretch the web adjacent the formed hems, with the draw tapes therein, prior to forming the seals at the formed hems.
A still further object is to electrostatically pin the formed hems to an underlying support, and to carry the thus pinned hems along the processing line on an intervening belt, thus controlling the transverse positioning of the hem with respect to hem sealing apparatus, for forming the hem seals.
A further object is to provide an angled turning member for assisting in returning the edge regions of the top and bottom layers into surface-to-surface contact with each other after the hem seals are formed along parallel paths.